What is the technical challenge of accurately achieving white balance in night videography when encountering multiple mixed artificial light sources (e.g., LED, incandescent, sodium vapor)?

Achieving accurate white balance in night videography when encountering multiple mixed artificial light sources presents a significant technical challenge because each light source emits light with a distinct color temperature and spectral power distribution, which cannot be simultaneously corrected by a single camera setting. White balance is the process of adjusting colors in an image so that objects that appear white in reality are rendered as white in the video, ensuring all other colors appear naturally. This correction accounts for the color cast introduced by various light sources. Different light sources produce light with different color temperatures, measured in Kelvins (K). Light with a lower Kelvin value appears warmer (more orange/red), while light with a higher Kelvin value appears cooler (more blue). The problem arises at night because a single scene often contains light from multiple sources like incandescent, sodium vapor, and LED, each with its unique characteristics.

Incandescent lights, such as older streetlights or home lights, emit a very warm, yellowish-orange light, typically around 2700K to 3000K. Their spectral power distribution, which describes the amount of light emitted at each wavelength, is continuous but heavily skewed towards the red and orange end of the spectrum, with less blue light. Sodium vapor lights, commonly found in older street lighting, present an even greater challenge. High-Pressure Sodium (HPS) lamps are very warm, orange-yellow, around 2000K-2200K, but have a highly discontinuous spectrum, meaning they emit light at specific, narrow wavelength bands and are missing significant portions of the visible spectrum. Low-Pressure Sodium (LPS) lamps are even more monochromatic, appearing almost pure orange-yellow. This spectral discontinuity fundamentally prevents accurate color rendition because objects whose colors depend on the missing wavelengths simply cannot reflect those colors and will appear desaturated or shifted in hue, regardless of white balance. For instance, a red object under a pure sodium vapor light will appear dark or brown because no red light is present for it to reflect. Modern LED lights are versatile, able to produce various color temperatures (e.g., warm white 3000K, neutral white 4000K, cool white 5000K-6000K). However, most white LEDs achieve 'white' light by using a blue LED with a yellow phosphor, resulting in a spiky and often uneven spectral power distribution. While they can achieve good overall color temperature, their specific spectral gaps or peaks can still lead to inaccuracies in rendering certain hues, and their Color Rendering Index (CRI), a measure of how accurately a light source renders colors compared to natural daylight, can vary widely.

The technical challenge manifests in several ways. Firstly, a videographer must choose a single white balance setting for the entire video frame. When one area is illuminated by warm incandescent light, another by cool LED light, and a third by orange sodium vapor light, setting a white balance to neutralize one source will inevitably miscolor the others. If balanced for the warm incandescent, the LED-lit areas will appear excessively blue; if balanced for the cool LED, the incandescent areas will look unnaturally orange. Secondly, the fundamental differences in spectral power distribution mean that even if the color temperature could be averaged, the camera cannot create light that simply isn't present in the scene. A red object under a sodium vapor lamp, which emits virtually no red light, cannot be made to look red through white balance adjustments, because there is no red information to correct. This is not merely a color temperature shift but a complete absence of certain wavelengths. Automatic White Balance (AWB) systems in cameras struggle immensely with this. They attempt to find a neutral point by analyzing the overall scene, but with conflicting color temperatures and discontinuous spectra, there is no single 'correct' neutral point. The AWB will either average the sources, creating a compromise that leaves all areas somewhat off, or lock onto the dominant source, severely miscoloring other parts of the scene. Manual white balance also faces this impossibility; the videographer must make a creative compromise, perhaps prioritizing accurate skin tones or neutralizing the most prominent light source, knowing that other areas will remain inaccurately rendered. The camera's sensor captures the light as it is, and a single global adjustment cannot simultaneously correct for multiple, fundamentally different light spectrums and color temperatures within the same frame.